To better support voice and packet data services in a wireless communications system, a traffic channel, by which a plurality of mobile stations communicates with a base station, is shared among the plurality of mobile stations. Transmission on the traffic channel is scheduled by the base station, based on channel condition information sent by the mobile stations on a reverse link. The sharing of the channel may be achieved using FDMA, TDMA, CDMA, or OFDMA techniques.
A Forward link Shared Signaling Channel (F-SSCH) carries a number of signaling messages that allocate or de-allocate different resources for a traffic channel, to or from a given mobile station. A collection of forward link signaling messages, developing in conjunction with the evolution of cdma2000 air interface standards, is illustrated in Table 1. Columns in Table 1 indicate different fields in a message, while rows correspond to different signaling messages. Every cell in Table 1 indicates multiplicity of a given field. A 3-bit Message (Mssg.) Type field allows a mobile station to identify the type of message, and therefore properly interpret subsequent fields. The set of information bits of every valid message is extended by a 16-bit cyclic redundancy check (CRC) to enable reliable detection.
TABLE 1Mssg.Ext.FieldtypeMACIDStickyChanIDPFTXTimingSuppl.Rank# bits391641612Access00010000100GrantFLAM00101111010RLAM01001111010MCW FLAM101101111010MCW FLAM210000030000SCW FLAM10101111011
The first type of message carries an Access Grant message, and is used to acknowledge an access attempt by a mobile station, to assign a new MACID, and to supply a 6-bit timing adjustment for the mobile station—so that it may align its reverse link transmission with reverse link timing of a base station.
The remaining messages are forward link and reverse link assignment messages, and all have a “sticky”, or persistent, bit that indicates whether an assignment is only for one packet, or lasts until explicitly de-assigned or lost due to packet failure. All of these assignment messages are also scrambled with the MACID of the target mobile station.
A forward link assignment message (FLAM) signals a forward link resource assignment to an active mobile station with resources assigned indicated by Channel Index (ChanID), and spectral efficiency indicated by Packet Format (PF). Whenever set, the Supplemental (Suppl.) assignment flag indicates an incremental assignment if the ChanID is not part of the existing assignment, or indicates a decremental assignment otherwise. A new assignment replaces an existing one if the Supplemental assignment flag is not set. The reverse link assignment message (RLAM) signals reverse link resource assignments, in a fashion identical to the FLAM.
A multi-codeword (MCW) FLAM is a forward link assignment message that may be used for mobile stations in the Multiple Input Multiple Output (MIMO) multi-codeword mode. Unlike the other assignment messages, this message indicates four packet formats corresponding to (at most) four MIMO layers (code words). This assignment message is split into two parts, namely MCW FLAM1 and MCW FLAM2, as shown in Table 1.
In the event when the number of layers in use is less than four, remaining PF fields are set to zero. A single-codeword (SCW) FLAM for MIMO operation is similar to the FLAB, except that it also indicates rank of the MIMO transmission. In addition, the Message Types of “110” and “111” are not used and are reserved.
Many, if not most, messages in Table 1 span between 31 and 34 bits, including 16-bit CRC. Based on this, all messages can be padded to a target or maximum number of bits (e.g., 34) with a relatively low efficiency loss. For example, the Access Grant message illustrated in Table 1 has a total length of 34 bits, including 16-bit CRC; and therefore no padding bit is needed for this Access Grant message. The FLAM message illustrated in Table 1 has a total length of 32 bits, including 16-bit CRC; and therefore requires two padding bits. Having a unified size for all signaling messages is convenient when all messages are encoded and modulated separately, since it removes overhead associated with indicating message sizes.
Conventional padding schemes add some type of Reserved Bits field—which typically consists of all “0” bits—at the end of a variable-length message body; in order to make total length of the message fixed. Prior Art FIG. 1 illustrates a conventional structure of message FLAM 100, corresponding to the example of Table 1.
Referring to FIG. 1, message FLAM 100 consists of a 3-bit Message (or Block) Type 110, a 1-bit Sticky 120 flag, a 6-bit Channel ID (ChanID) 130, a 4-bit Packet Format (PF) 140, a 1-bit Extended Transmission (Ext. Trans.) 150, and a 1-bit Supplement 160 flag. A 2-bit Reserved (Rsvd) Bits 170 is padded at the end of the message body. In addition, a 16-bit CRC is added after the reserved bits to make total length of the message 34 bits. Reserved Bits 170 are set to “00”. As a result, “00”, “10”, and “11” are not used on Reserved Bits 170, and may be reserved for future usage.
Unfortunately, however, this method causes un-used and reserved message numbering space to be fragmented. For example, the message numbering space that can be represented with “001xxxxxxxxxxx00” is used for FLAM, where “x” can be “0” or “1”. The message numbering spaces that can be represented with “001xxxxxxxxxxx01” and “001xxxxxxxxxxx1x” are reserved, where “x” can be “0” or “1”—but these spaces are fragmented. Thus it may be inefficient or inconvenient to add new signaling messages on the F-SSCH in the future, using such fragmented reserved numbering space.